Field of the Invention
Embodiments of the invention generally relate to electronics, and in particular, to apparatuses that include memory cells such as phase-change memory (PCM) cells.
Description of the Related Art
Phase-change memory (PCM), also known as PCRAM or PRAM, is a form of non-volatile memory made from a phase-change material. An example of a phase-change material is Germanium-Antimony-Tellurium (GST). When a cell of GST material is heated beyond its melting point and cools relatively rapidly, the phase-change material of the cell is in an amorphous state and can have a resistance associated with a first state, such as logic 0. When the cell of GST material is heated and is cooled relatively slowly, the phase-change material of the cell is in a crystalline state and can have a resistance associated with a second state, such as logic 1. The cell of GST material can also be heated to a relatively lower temperature, such as a temperature associated with crystallization to achieve the crystalline state. Intermediate states are also possible for multi-level cells.
For relatively good density and low cost, the individual cells of a memory device will be small. However, perfect uniformity during production is not practical, and even relatively small differences in size can result in a relatively large amount of variability in the appropriate amount of power that should be used to heat a cell. In addition, other sources of variability exist. Some sources of variability can affect an entire array of cells. While it is possible to compensate for some sources of variability by a calibration procedure performed during manufacturing, such procedures tend to be time consuming, which can increase the cost of production.
To avoid repetition of description, components having the same or similar function may be referenced by the same reference number.